This proposal will focus on using the honeybee (Apis mellifera) as a model animal species for understanding mechanisms of behavioral plasticity toward odors. These animals are faced with the same types of olfactory problems as mammals. They require the capability to detect and respond to a very large number of odors because they depend on locating many different types of flowers to harvest carbohydrate resources in nectars. Association of these odors with nectar changes many times within an individual's lifetime, which also requires that animals learn about these associations. Like mammals, insects exhibit a variety of means to learn about and encode memories for floral odors. Comparative evidence indicates that behavioral and systems-level neural processing similarities between insects and mammals have evolved independently. That suggests that there may only be one general neural solution available to encode information about odors. Therefore, as comparative models, insects can be critical for revealing how odors are learned and encoded in the CNS, and whether this mechanism is fundamental to olfactory processing. The aims of this proposal are to evaluate mechanisms of neural plasticity that exist in the insect Antennal Lobes (AL), which are the neural analogs to the mammalian Olfactory Bulb (Hildebrand &Shepherd 1997). The central theme is that documented neural mechanisms and modulatory pathways in the AL that represent the presence (or absence) of reinforcement serve as a means to filter out unimportant, variable background odors. This allows biologically relevant, learned odors to be readily detected. There will be three aims. First, behavioral investigations will examine in detail mechanisms that underlie a learned inattention (CS preexposure effect) toward odors and blocking in odor-odor mixtures. In particular, manipulations of the conditioning context will reveal the extent to which specific theoretical treatments of CS preexposure can account for it in insects. Second, multichannel recording techniques will be employed to investigate whether and how these behavioral mechanisms may be implemented as a filtering mechanism in the AL. Third, pharmacological and molecular manipulation by way of RNA interference will be used to examine how modulatory pathways represent reinforcement in the AL by regulating biogenic amine (serotonin and octopamine) release.